276 Warren — Ilmenite Rocks near St. Urbain, Quebec; 



The texture of the rocks are thought to represent substantially 

 that which developed upon crystallization from a magmatic con- 

 dition. Like so many anorthosites the present one has un- 

 doubtedly been subjected to more or less dynamic action, but 

 it does not seem to have been particularly severe about and in 

 the ilmenite rocks. The r utile grains show no sign of strains 

 nor crushing. Granting for the ilmenite-hematite intergrowth 

 a secondary origin, which is open to question, its development 

 could not have much, if at all, modified the original texture 

 of the rock. The feldspar also shows but little evidence of 

 severe strains or crushing. Furthermore, if we assume that 

 both the sapphirine and the biotite are due to secondary reac- 

 tions, during or subsequent to the actual crystallization of the 

 magma, the changes involved are clearly incompetent to account 

 for the formation of the rutile as a secondary mineral ; nor is 

 there any other evidence of mineralization or chemical changes 

 adequate to produce it. It is, furthermore, most unlikely that 

 if the rutile is of secondary origin its occurrence would be 

 confined to portions of the mass, the remainder of which has 

 been most surely subjected to the same dynamic and metamor- 

 phic action. 



It is believed that the rutile-sapphirine-bearing rock repre- 

 sents a magmatic crystallization, and as such it is a new and 

 extreme ultra-basic type, which is deserving of a distinct name. 

 Accordingly the name Urbainite is proposed for it, with the 

 expectation that the same stem will be used with an appropri- 

 ate termination for its designation in the " Quantitative Sys- 

 tem " so soon as fresh material can be secured for a satisfactory 

 chemical analysis. 



Without going into a discussion of the question here, the 

 writer ventures to express the opinion, founded in part on the 

 texturaland mineralogical evidence above presented, that these 

 masses of ilmenite rock, if they are, as now believed, products 

 of magmatic differentiation, have crystallized as units from 

 partial magmas of like composition to the resulting rocks sub- 

 sequent to their differentiation from the parent anorthosite 

 magma, and that they have not been formed by the gradual 

 accumulation of separate grains through a process of fractional 

 crystallization, 



Summary. 



I. — Large masses of rock consisting largely of titanic-iron 

 ore occur in anorthosite in the Parish of St. Urbain, Province 

 of Quebec, Canada. These masses have in general an elongate 

 form, sometimes dike-like, conforming to the structure of the 

 enclosing rock. 



II. — In the main they consist of ilmenite, hematite, with 

 accessory andesine, green spinel and biotite. Throughout a con- 



